Wearable Fingernail-Based Microfluidic Paper Analytical Device for Naked-Eye Detection of γ-Hydroxybutyric Acid in Beverages

Drug-facilitated sexual assault (DFSA) remains a critical public safety concern, with γ-hydroxybutyric acid (GHB) being one of the most frequently used substances due to its odorless, colorless, and tasteless properties, which make it nearly undetectable in beverages. As GHB can quickly induce sedation and is rapidly eliminated from the body, there is an urgent need for practical and preventive detection tools that empower potential victims. In this study, we present a wearable fingernail-based microfluidic paper analytical device (PAD) that allows users to rapidly and visually detect GHB in beverages prior to consumption. The device features a Fe³⁺-based colorimetric sensing reaction embedded in a microfluidic paper strip affixed to a fingernail, enabling effortless sampling by simple dipping. In the presence of GHB, Fe³⁺ forms a stable complex, preventing its reduction by hydroxylamine and inhibiting the formation of the orange Fe²⁺-phenanthroline chromophore─resulting in a clear, observable color change from orange to colorless (within 15 min). The sensor provides a detection limit of 0.55 μg mL^-1 (digital analysis) and a naked-eye cutoff at 10 mg mL^-1. This low-cost, instrument-free, and highly portable sensor successfully detects GHB in both alcoholic and nonalcoholic beverages, demonstrating its potential as a user-friendly screening tool for real-world application in social settings, promoting personal safety and DFSA prevention.